Rathite Ag2Pb12-xTlx/2As18+x/2S40

Crystal Data: Monoclinic. Point Group: 2/m. Crystals prismatic to short prismatic and striated parallel to [100]. Twinning: Polysynthetic on {001}in some material.

Physical Properties: Cleavage: Perfect on {001}; parting on {010}. Fracture: Subconchoidal. Hardness = 3 VHN = 161 D(meas.) = 4.986-5.446 (varies with Tl content) D(calc.) = 5.31

Optical Properties: Not fully opaque. Color: Lead-gray, may tarnish to iridescence; grayish white in reflected light with deep red internal reflections. Streak: Chocolate-brown. Luster: Metallic to dull. Pleochroism: Strong. Anisotropism: Intense; olive-green or yellow and bluish violet. R1-R2: (400) 40.0-45.2, (420) 39.2-44.8, (440) 38.4-44.3, (460) 37.8-43.7, (480) 37.2-43.7, (500) 36.6-42.8, (520) 36.0-42.3, (540) 35.4-41.8, (560) 34.7-41.0, (580) 34.0-40.2, (600) 33.3-39.3, (620) 32.6-38.4, (640) 31.9-37.6, (660) 31.3-36.7, (680) 30.7-35.9, (700) 30.2-35.2

Cell Data: Space Group: P21/c. (Tl-poor) a = 8.471(2) b = 7.926(2) c = 25.186(5) β = 100.58(3)° Z = 1; (Tl-rich) a = 8.521(2) b = 8.005(2) c = 25.031(5) β = 100.56(3)° Z = 1

X-ray Powder Pattern: Binntal, Switzerland. 2.75 (100), 3.60 (80), 3.39 (70), 2.87 (70), 4.19 (60), 2.97 (60), 2.22 (50)

Chemistry: (1) (2) (3) Pb 36.61 47.24 27.33 Tl 5.36 0.16 11.78 Ag 4.13 3.35 3.75 As 27.31 21.76 29.28 Sb 1.94 3.89 2.16 S 24.48 23.55 25.35 Total 99.82 99.95 99.65

(1) Binntal, Switzerland; by electron microprobe, average of 11 analyses; corresponds to Ag2.00Tl1.36Pb9.24(As19.08Sb0.84)Σ=19.92S40.00. (2) Lengenbach quarry, Switzerland; electron microprobe analysis; corresponds to Ag1.70Tl0.04Pb12.47(As15.88Sb1.75)Σ=17.63S40.17. (3) Lengenbach quarry, Switzerland; electron microprobe analysis; corresponds to Ag1.76Tl2.91Pb6.67(As19.77Sb0.90)Σ=20.66S39.99.

Occurrence: In crystalline dolostone with other Pb-As-S minerals.

Association: Liveingite, baumhauerite, sartorite, hutchinsonite, dufrénoysite, tennantite, pyrite.

Distribution: From the Lengenbach quarry [TL] and at Reckibach, Binntal, Valais, Switzerland.

Name: Honors Gerhard von Rath (1830-1888), Professor of Mineralogy, Bonn, Germany.

Type Material: University of Fribourg, Fribourg, Switzerland, B742.

References: (1) Palache, C., H. Berman, and C. Frondel (1944) Dana’s system of mineralogy, (7th edition), v. I, 455-457. (2) Marumo, F. and W. Nowacki (1965) The crystal structure of rathite-I. Zeits. Krist., 122, 433-456. (3) Berlepsch, P., T. Armbruster, and D. Topa (2002) Structural and chemical variations in rathite, Pb8Pb4-x(Tl2As2)x(Ag2As2)As16S40: modulations of a parent structure. Zeits. Krist., 217, 581-590. (4) (2004) Amer. Mineral., 89, 471 (abs. ref. 3). (5) Berry, L.G. and R.M. Thompson (1962) X-ray powder data for the ore minerals. Geol. Soc. Amer. Mem. 85, 152- 153. (6) Criddle, A.J. and C.J. Stanley, Eds. (1993) Quantitative data file for ore minerals, 3rd ed. Chapman & Hall, London, 475. (7) Topa , D. and U. Kolitsch (2018) The crystal chemistry of rathite based on new electron-microprobe data and single-crystal structure refinements: the role of thallium. Minerals, 8, 466.

Mineralogical Society of America Handbook of Mineralogy Revised 1/10/2021